The present invention relates to optical lithography, particularly to the fabrication of integrated circuit components (IC) utilizing optical lithography, and more particularly to an extreme ultraviolet lithography machine using 10-14 nm extreme ultraviolet photons for initial chip size fabrication of 100 nm, reduced from current 0.25 microns, with scaling down to possibly 30 nm.
For nearly 3 decades, the number of transistors contained on an IC has grown exponentially, doubling on the average of every 18 months. In the early 1990's the Semiconductor Industry Association (SIA) developed the first national technology roadmap outlining the equipment and technology needs for continuing to support the increase in IC complexity. With each new technology generation, lithography has become an even more important key driver for the semiconductor industry because of smaller feature sizes and tighter overlay requirements and also because of the increasing lithography tool costs relative to total manufacturing costs. Although conventional optical lithography is expected to support the roadmap through the end of the decade, new approaches will be required to support manufacturing of 100 nm size chip technologies, currently at 0.25 microns, beyond the year 2004.
A major industry direction has focused on the possible development of cameras to print sub 130 nm features with a greater process latitude than afforded by 248 nm or 193 nm cameras. This has led to considering 157 nm, 126 nm and 13 nm wavelengths for which there are potentially useful illumination sources. The advantage of migrating to shorter wavelengths is that, for constant resolution and k.sub.1 (an imperical process dependent parameter), depth of focus (DOF) scales inversely with wavelength.
Below 193 nm wavelengths transmissive optical elements composed of fused silica exhibit high losses and alternate materials must be considered. Although CaF.sub.2 and LiF.sub.2 materials have been identified for possible use in 157 nm and 126 nm systems, materials issues associated with quality, size and stability tend to preclude the design of a transmissive system. In addition, large NA (numerical aperture) systems would be required, since both 157 nm and 126 nm systems provide only marginal advantage in terms of the required k.sub.1 over a 193 nm system with an NA of 0.6. A 157 nm system provides only a 20% larger DOF than a 193 nm system for the same resolution. Because of the high transmissive losses, all reflective imaging systems and use of CaF.sub.2 must be utilized; these cameras will require five or more mirrors. The mirrors must be steep and highly aspheric to avoid obscuration of the light beams (the mirrors tend to get in the way of one another) and the used portions of many mirrors will be located far off the axis of the optical system. Generally speaking, as the NA of the camera is increased, the used mirror segments move further off axis and the mirror asphericity must be increased to compensate for the aberrations induced by non-normal incidence angles. In a recent Sematech meeting on "All-Reflective Imaging Systems for 0.13 Micron Lithography" it was reported that the aberrations, which must be compensated for with asphericity, grow at a relatively high power of the camera NA, at least as (NA). As NA increases, the mirrors become larger and more aspheric. Aspheric departures from a best fit sphere become very large, more than 100 microns for systems with NA's in excess of 0.5. As a result, there seems to be general agreement that all-reflective systems for 157 nm and 126 nm having NAs as large as 0.5 are not manufacturable on the time scale required. Alternately, 13 nm imaging systems can operate at small NA, from 0.1 to 0.2, and achieve the necessary resolution.
The first papers proposing the use of soft x-ray or EUV radiation (wavelengths from 2 nm through 50 nm) for projection lithography were published in 1988. Lithography systems for use at 4.5 nm and 15.37 nm were described by research groups from Lawrence Livermore National Laboratory (LLNL) and Bell Laboratory, respectively. Both research groups described all-reflective projection lithography systems using multilayer-coated mirrors and reflection masks. Shortly thereafter in 1989, a Japanese research group demonstrated projection imaging of 0.5 micron features using 13 nm radiation and Mo/Si multilayer reflective coatings on a reflection mask and on the camera mirrors. The first demonstration of the technology's potential and of nearly diffractive-limited imaging followed in 1990 with the printing of features as small as 50 nm in PMMA resist using 13 nm radiation by the Bell Laboratory group. Interest in the technology, originally called soft x-ray projection lithography (SXPL), grew rapidly spurred by a number of focused workshops and topical meetings. In the U.S. the efforts at LLNL and Bell Laboratory increased, and major research groups at Sandia National Laboratories (SNL) and at Lawrence Berkeley National Laboratory (LBNL) joined this effort. The various research groups established advisory boards with strong participation by the lithography tool manufacturers and the IC manufacturers to provide oversight and guidance for the development work. Emphasis was placed on the work relevant to industry needs. It also became apparent that SXPL was being confused with proximity x-ray lithography. As a result, the name of the technology was changed to extreme ultraviolet (EUV) lithography. In the 1995-96 time frame, the various research groups worked to coalesce their work into a single "national program". Simultaneously, support for technology transfer within the national laboratories (LLNL, SNL and LLBL) and for lithograph research within Bell Laboratory declined. In the meantime, research personnel within the semiconductor industry became convinced that the EUVL technology was demonstrating great promise. As a result, a consortium of semiconductor manufacturers, the EUV Limited Liability Company (EUVLLC), composed of Advanced Micro Devices, Motorola, and Intel Corporation, was formed to provide funding and guidance for the development of EUVL within the national laboratories. At the same time, the previously independent EUVL research groups with LLNL, SNL, and LBNL joined together to form a "Virtual National Lab" (VNL), working as a single entity with combined efforts to implement the EUVL concept, which is an extension of optical lithography to dramatically shorten wavelengths (10-14 nm, particularly 13 nm).
Extreme ultraviolet lithography (EUVL), using 10-14 nm extreme ultraviolet photons, is one promising technology which builds on the industrial optical experience, since it is an extension of optical lithography to dramatically shorten wavelengths. Initially this EUVL technology will support IC fabrication at 100 nm. Scaling is expected to support several technology generations down to possibly 30 nm.
There are several advantages of EUV lithography over other technologies. EUV parallels and builds on the conventional optical lithography experience base. 1) Imaging follows the trends of conventional optics in terms of resolution and depth of focus with numerical aperture (NA) and is expected to scale down to 30 nm. 2) The 4.times. masks are fabricated on robust substrates, not membranes, and are easier to write than 1.times. or segmented masks, and use conventional silicon processing to define the final geometric patterns on the mask. 3) The use of low NA optics provides good depth of focus for isolated and dense lines simultaneously, minimizing the need for mask biasing. 4) The technology provides a granular tool solution when a laser produced plasma or other discrete source is used. 5) Photo-resists used by the 193 nm technology are extendable to EUV wavelengths (10-14 nm). 6) The technology is fully compatible with larger circuit design rules and could be introduced selectively at 130 nm. In addition, the x-ray syorchrotron sources may be used for EUVL with an appropriate condenser design.
The present invention involves an EUVL machine or system for wavelengths in the 10-14 nm range, and particularly the 13 nm region. The EUVL machine of this invention encompasses an evacuated source chamber and a main projection chamber. In the illustrated embodiment, the main or projection chamber is mounted on a support block and the chambers are connected by a transport tube, with each of the chambers having a separate vacuum system. In the illustrated embodiment, the light beam from a laser source to the substrate is reflected nine time, with four of the reflective optics being mounted in a projection optics box located in the projection or main chamber between the reticle and the wafer or substrate. The projection optic box and the wafer support structure are provided with vibration isolators.